It is known that the internal resistance of a lambda sensor drops significantly with increasing temperature. There is a definite relationship between the sensor temperature and the internal resistance. This relationship is used to determine the sensor temperature from a measurement of the internal resistance, as described, for example, in U.S. Pat. No. 4,419,190.
The temperature of the lambda sensor is determined in the case of an unheated sensor exclusively and in the case of a heated sensor predominantly by the temperature of the exhaust gas surrounding it. This temperature is determined according to the state of the art with the aid of a separate measuring sensor.
It is the object of the invention to specify methods for determining the temperatures of a lambda sensor and/or of the exhaust gas surrounding it with the methods being simple but nevertheless operating precisely. Furthermore, the invention is based on the object of specifying an apparatus of simple configuration for determining the exhaust gas temperature.